<html>
<script>
function sizeResizer() {
    // reference resizer
    var img = document.getElementsByTagName("img")[0];
    // hidden textarea
    var textarea = document.getElementsByTagName("textarea")[0];
    var width = 200 - textarea.clientWidth;
    var height = 200 - textarea.clientHeight;
    // (Leave test failing if a scrollbar is missing)
    if (width != 0 && height != 0) {
        img.style.width = width + "px";
        img.style.left = textarea.clientWidth + "px";
        img.style.height = height + "px";
        img.style.top = textarea.clientHeight + "px";
    }
}
</script>
<body onload="sizeResizer()">
<textarea style="width: 200px; height: 200px; margin: 0; border: none;
                 background: red; font-size: 400px;">
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</textarea>
<div style="position: relative; top: -200px;
            width: 200px; height: 200px; margin: 0; border: none;
            background: lightgreen">
  <img style="position: relative;" src="chrome://global/skin/icons/resizer.png">
</div>
</body>
</html>
